System and method for spinal implant placement

ABSTRACT

A posterior spinal fusion system may include a plurality of cannulas that mate with cages polyaxially coupled to pedicle screws. The cannulas maintain access to the pedicle screws to facilitate percutaneous insertion of a fusion rod into engagement with the cages. Each cannula has a pair of blades that may be held together by an abutment member that at least partially encircles the blades. Each abutment member abuts the skin to define a variable subcutaneous length of the corresponding cannula. Each abutment members is also lockably removable from the corresponding blades to enable the blades to pivot with respect to the connecting element to a position in which they can be withdrawn from the connecting element. The blades of each cannula are spaced apart to provide first and second slots of each cannula, through which the fusion rod can be percutaneously inserted.

CROSS-REFERENCE TO RELATED APPLICATIONS

ThisNotice: More than one reissue application has been filed for thereissue of U.S. Pat. No. 8,002,798. The reissue applications are U.S.application Ser. No. 15/620,402, U.S. application Ser. No. 14/824,951,U.S. application Ser. No. 13/973,462, U.S. application Ser. No.13/972,493, and the present application. The present application is acontinuation reissue of U.S. application Ser. No. 15/620,402, filed onJun. 12, 2017, which is a continuation reissue of U.S. application Ser.No. 14/824,951, filed on Aug. 12, 2015, which is a continuation reissueof U.S. application Ser. No. 13/973,462, filed on Aug. 22, 2013, whichis a continuation reissue of U.S. application Ser. No. 13/972,493 filedon Aug. 21, 2013, which is an application for reissue of U.S. Pat. No.8,002,798, which is a continuation-in-part of U.S. application Ser. No.10/868,075, filed on Jun. 15, 2004, which claims the benefirbenefit ofU.S. Provisional Application No. 60/518,580, filed Nov. 8, 2003, thedisclosuredisclosures of which are incorporated herein by reference.This application claimU.S. Pat. No. 8,002,798 claims the benefit of U.S.Provisional Application No. 60/682,783, filed on May 19, 2005, thedisclosure of which is incorporated herein by reference.

This application relates to U.S. Application Ser. No. 10/669,927, filedon Sep. 24, 2003, the disclosure of which is hereby incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates generally to implantable devices, and moreprecisely, to posterior spinal fusion systems.

2. The Relevant Technology

Many people experience joint pain in one form or another. In particular,back pain may result from the occurrence of a wide variety of spinalpathologies. Some such pathologies are currently treated by fusingadjacent vertebrae to prevent their relative motion. According to oneknown method, pedicle screws are implanted in the pedicles and arerigidly secured to a rod passing posterior to the pedicles.

Unfortunately, current procedures often involve the exposure of arelatively large area to permit implantation of the rod. Some currentprocedures cannot be used to implant a rod that secures more than twovertebrae together. Other known procedures are somewhat complex, andtherefore require many parts and surgical steps. Accordingly, there is aneed for new fusion rod implantation systems and methods that remedy theshortcomings of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope.

FIG. 1 is a perspective view of two adjacent vertebrae of a spine, withguide wires implanted in the pedicles of the right side.

FIG. 2 is a perspective view of three guide wires in isolation,positioned as though implanted in the pedicles of the right sides ofthree adjacent vertebrae.

FIG. 3 is a perspective view of the guide wires of FIG. 2, with dilatorsadvanced along the guide wires to dilate surrounding tissue.

FIG. 4 is a perspective view of the guide wires and dilators of FIG. 3,with hollow dilators placed around the solid dilators.

FIG. 5 is a perspective view of the guide wires and hollow dilators ofFIG. 4, with the solid dilators removed.

FIG. 6 is a perspective view of the guide wires and hollow dilators,with a tapping tool placed over one of the guide wires to tap thecorresponding pedicle.

FIG. 7 is an exploded, perspective view of a cannula, abutment member,pedicle screw, cage, set screw, and a portion of a rod according to oneembodiment of the invention.

FIG. 8 is a perspective view of the cannula, abutment member, pediclescrew, cage, set screw, and rod portion of FIG. 7, in assembled form.

FIG. 9 is a perspective view of a screw insertion tool according to oneembodiment of the invention.

FIG. 10 is a perspective view of the screw insertion tool of FIG. 9, inengagement with the assembly of FIG. 8, excluding the rod portion andthe set screw.

FIG. 11 is a perspective view of the screw insertion tool in use toimplant the assembly of FIG. 8, excluding rod portions and set screws,over the first guide wire of FIG. 2.

FIG. 12 is a perspective view of a fascia clipping tool according to oneembodiment of the invention.

FIG. 13 is a perspective view of the fascia clipping tool of FIG. 12inserted into one of the cannulas of FIG. 11 to sever the adjoiningfascia.

FIG. 14 is a perspective view of a rod insertion tool according to oneembodiment of the invention.

FIG. 15 is a perspective view of the rod insertion tool of FIG. 14secured to a rod to facilitate manual insertion of the rod through thecannulas of FIG. 11.

FIG. 16 is a perspective view of a rod seating tool according to oneembodiment of the invention.

FIG. 17 is a perspective view of the rod seating tool of FIG. 16inserted into one of the cannulas of FIG. 11 to help seat the rod in thecages.

FIG. 18 is a perspective view of a rod holding tool according to oneembodiment of the invention.

FIG. 19 is a perspective view of the rod holding tool of FIG. 18inserted into one of the cannulas of FIG. 11 to further manipulate therod.

FIG. 20 is a perspective view of a set screw driver according to oneembodiment of the invention.

FIG. 21 is a perspective view of the set screw driver of FIG. 20inserted into one of the cannulas of FIG. 11 to tighten a set screw toretain the rod within the corresponding cage.

FIG. 22 is a perspective view of the pedicle screws, cages, set screws,and cannulas of FIG. 11, with the abutment members removed to permitremoval of the cannulas from the cages.

FIG. 23 is a perspective view of three adjacent vertebrae of the spine,with the rod secured to the pedicle screws to provide posterior spinalfusion.

FIG. 24 is a perspective view of a cannula and cage according to onealternative embodiment of the invention, in which the cannula is securedto the cage by two frangible couplings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to systems and methods for implantation oforthopedic devices. Although the examples provided herein generallyrelate to insertion of a rod for a posterior spinal fusion system, thepresent invention may be applied to any procedure in which a device isto be implanted in the body in a minimally invasive manner. Accordingly,the scope of the present invention is not intended to be limited by theexamples discussed herein, but only by the appended claims.

As used herein, a “cannula” is an elongated structure having a hollowinterior that provides communication between opposite ends of theelongated structure. A “subcutaneous length” is the portion of an objectthat lies below the surface of a patient's skin. “Transverse” refers toan object or direction that is not parallel with, and not nearlyparallel with, another object or direction. A “connecting element” isany man-made structure that is implantable to remain in the body, and isconnectable to an anatomic feature and/or another implantable structure.The term “percutaneous” refers to an action carried out at leastpartially underneath unbroken skin.

The term “discrete” refers to parts that are not formed as a singlepiece, but are separate pieces from each other. The term “coupled”refers to two elements that are secured together, whether they have beenformed separately and secured together via a secondary operation, orthey have been formed as a single piece (i.e., formed in a coupledstate). The term “securable” refers to elements that are capable ofbeing coupled together, or are already coupled together. A “blade” is anelongated, thin structure. “Polyaxial motion” refers to motion along orabout multiple orthogonal axes.

Referring to FIG. 1, a perspective view illustrates a portion of a spine10. FIG. 1 illustrates only the bony structures; accordingly, ligaments,cartilage, and other soft tissues are omitted for clarity. The spine 10has a cephalad direction 12, a caudal direction 14, an anteriordirection 16, a posterior direction 18, and a medial/lateral axis 20,all of which are oriented as shown by the arrows bearing the samereference numerals. In this application, “left” and “right” are usedwith reference to a posterior view, i.e., a view from behind the spine10. “Medial” refers to a position or orientation toward a sagittal plane(i.e., plane of symmetry that separates left and right sides from eachother) of the spine 10, and “lateral” refers to a position ororientation relatively further from the sagittal plane.

As shown, the portion of the spine 10 illustrated in FIG. 1 includes afirst vertebra 24, which may be the L5 (Fifth Lumbar) vertebra of apatient, and a second vertebra 26, which may be the L4 (Fourth Lumbar)vertebra of the patient. The systems and methods may be applicable toany vertebra or vertebrae of the spine 10 and/or the sacrum (not shown).In this application, the term “vertebra” may be broadly interpreted toinclude the sacrum.

As shown, the first vertebra 24 has a body 28 with a generally disc-likeshape and two pedicles 30 that extend posteriorly from the body 28. Aposterior arch, or lamina 32, extends between the posterior ends of thepedicles 30 to couple the pedicles 30 together. The first vertebra 24also has a pair of transverse processes 34 that extend laterally fromthe pedicles 30 generally along the medial/lateral axis 20, and aspinous process 36 that extends from the lamina 32 along the posteriordirection 18.

The first vertebra 24 also has a pair of superior facets 38, which arepositioned toward the top of the first vertebra 24 and face generallymedially. Additionally, the first vertebra 24 has inferior facets 40,which are positioned toward the bottom of the first vertebra 24 and facegenerally laterally. Each of the pedicles 30 of the first vertebra 24has a saddle point 42, which is positioned generally at the center ofthe juncture of each superior facet 38 with the adjacent transverseprocess 34.

Similarly, the second vertebra 26 has a body 48 from which two pedicles50 extend posteriorly. A posterior arch, or lamina 52, extends betweenthe posterior ends of the pedicles 50 to couple the pedicles 50together. The second vertebra 26 also has a pair of transverse processes54, each of which extends from the corresponding pedicle 50 generallyalong the medial/lateral axis 20, and a spinous process 56 that extendsfrom the lamina 52 along the posterior direction 18.

The second vertebra 26 also has a pair of superior facets 58, which arepositioned toward the top of the second vertebra 26 and face generallyinward. Additionally, the second vertebra 26 has inferior facets 60,which are positioned toward the bottom of the second vertebra 26 andface generally outward. Each of the pedicles 60 of the second vertebra26 has a saddle point 62, which is positioned generally at the center ofthe juncture of each superior facet 58 with the adjacent transverseprocess 54.

The superior facets 38 of the first vertebra 24 articulate (i.e., slideand/or press) with the inferior facets 60 of the second vertebra 26 tolimit relative motion between the first and second vertebrae 24, 26.Thus, the combination of each superior facet 38 with the adjacentinferior facet 60 provides a facet joint 64. The first and secondvertebrae 24, 26 thus define two facet joints 64 that span the distancebetween the first and second vertebrae 24, 26. The inferior facets 40 ofthe first vertebra 40 and the superior facets 58 of the second vertebra26 are part of other facet joints that control motion between the firstand second vertebrae 24, 26 and adjacent vertebrae (not shown) and/orthe sacrum (also not shown).

The vertebrae 24, 26 and/or the intervertebral disc (not shown) betweenthem, may be damaged or diseased in some manner that makes it desirableto secure the vertebrae 24, 26 together in a manner that preventsrelative motion between them. Accordingly, posterior spinal fusion maybe employed to secure the pedicles 30, 50 together. FIGS. 1 through 23illustrate one system and method for installing a posterior spinalfusion system. FIG. 24 illustrates a cannula and cage according to onealternative embodiment of the invention.

As further illustrated in FIG. 1, a first guide wire 70 has beeninserted into the right-side pedicle 30 of the first vertebra 24, and asecond guide wire 72 has been inserted into the right-side pedicle 50 ofthe second vertebra 26. The guide wires 70, 72 pass through the saddlepoints 42, 62, respectively, of the pedicles 30, 50. Each of the guidewires 70, 72 has a proximal end 74 and a distal end 76. As shown, theproximal ends 74 are exposed, and the distal ends 76 are implanted inthe pedicles 30, 50. The distal ends 76 may be implanted by methodsknown in the surgical arts.

Referring to FIG. 2, a perspective view illustrates the first and secondguide wires 70, 72 of FIG. 1, with the vertebrae 24, 26 removed forclarity. A third guide wire 78 is also shown. The third guide wire 78 ispositioned adjacent to the first and second guide wires 70, 72 as thoughthe third guide wire 78 were implanted in the right-hand pedicle of avertebra (not shown) directly superior to the second vertebra 26.Accordingly, the method of FIGS. 1 through 23 may be used to securetogether vertebrae on multiple levels, not just two adjacent vertebrae.

Referring to FIG. 3, a perspective view illustrates the guide wires 70,72, 78, in conjunction with a first dilator 80, a second dilator 82, anda third dilator 88. Each of the dilators 180, 82, 88 has a proximal end92 and a distal end 94. The proximal ends 92 may be shaped for grippingby hand, or for attachment to a handle or the like. The distal ends 94are rounded to permit relatively gentle spreading of tissues surroundingthe guide wires 70, 72, 78 by the dilators 80, 82, 88.

Each of the dilators 80, 82, 88 has a bore sized to receive the proximalend 74 of the corresponding guide wire 70, 72, or 78, so that thedilators 80, 82, 88 are able to slide along the guide wires 70, 72, 78toward the distal ends 74, thereby spreading the tissues away from theguide wires 70, 72, 78. Each of the dilators 80, 82, 88 may optionallyinclude a plurality of nesting elements that permit discretely gradualdilation. As an alternative to the guide wires 70, 72, 78 and thedilators 80, 82, 88, a variety of other guiding devices and/or dilationdevices may be used within the scope of the present invention.

Referring to FIG. 4, a perspective view illustrates the guide wires 70,72, 78 and dilators 80, 82, 88 of FIG. 3, with first, second, and thirdhollow dilators 100, 102, 104 placed around the dilators 80, 82, 88,respectively. Each of the hollow dilators 100, 102, 104 has a generallytubular shape with a proximal end 106, a distal end 108, and a bore 110extending from the proximal end 106 to the distal end 108. Each of thebores 110 is sized to receive the outward-facing surface of thecorresponding dilator 80, 82, 88.

Accordingly, the hollow dilators 100, 102, 104 may simply slide alongthe anterior direction 16 between the outward-facing surfaces of thedilators 80, 82, 88 and the adjoining tissues. The hollow dilators 100,102, 104 then reach the positions shown in FIG. 4, thereby removing thedilators 80, 82, 88 from significant contact with the tissues to bedilated.

Referring to FIG. 5, a perspective view illustrates the guide wires 70,72, 78 and hollow dilators 100, 102, 104 of FIG. 4, with the dilators80, 82, 88 removed. The dilators 80, 82, 88 are simply withdrawn alongthe posterior direction 18 from within the hollow dilators 100, 102, 104to leave the bores 110 of the hollow dilators 100, 102, 104unobstructed.

Referring to FIG. 6, a perspective view illustrates the guide wires 70,72, 78 and hollow dilators 100, 102, 104, with a tapping tool 120 placedover the first guide wire 70 to tap the corresponding pedicle (not shownin FIG. 6). As shown, the tapping tool 120 may have a handle 122 shapedto be gripped by hand, and a shank 124 extending from the handle 122.The shank 124 has a proximal end 126 coupled to the handle 122 and adistal end 128 having a plurality of threads 130.

The tapping tool 120 also has a bore (not shown) extending through theshank 124 and through at least a portion of the handle 122. The bore issized to receive any of the guide wires 70, 72, 78 so that the tappingtool 120 can be guided sequentially along each of the guide wires 70,72, 78 to tap the pedicle 30 of the first vertebra 24, the pedicle 50 ofthe second vertebra 26, and the pedicle of the third vertebra (not shownin FIG. 6). Tapping is carried out by rotating the handle 122 clockwisewhile exerting axial pressure on the handle 122 to cause the distal end128 to penetrate the bone. After a pedicle has been tapped, the distalend 128 is withdrawn from the tapped cavity by rotating the handle 122counterclockwise.

Referring to FIG. 7, an exploded, perspective view illustrates aconnecting element 140, a cannula 142, an abutment member 144, and a rodportion 146 according to one embodiment of the invention. The rodportion 146 is a segment of a longer rod that may be used to secure thefirst vertebra 24, the second vertebra 26, and the third vertebra (notshown in FIG. 7) together. The connecting element 140 is used to securethe rod portion 146 to one pedicle of the vertebrae to be securedtogether. The cannula 142 is used to maintain access to the connectingelement 140 after it has been implanted in the pedicle in a manner thatfacilitates percutaneous placement of the rod portion 146 and attachmentof the rod portion 146 to the connecting element 140. The abutmentmember 144 helps to hold the cannula 142 together and keep it secured tothe connecting element 140 in a manner that will be describedsubsequently.

As embodied in FIG. 7, the connecting element 140 has a pedicle screw150, a cage 152, and a set screw 154. The pedicle screw 150 is theportion of the connecting element 140 that is implanted in thecorresponding pedicle. The pedicle screw 150 is able to hold the cage152 against the pedicle at any of a variety of orientations of the cage152 with respect to the pedicle screw 150. Thus, the cage 152 ispolyaxially movable with respect to the pedicle screw 150 until the setscrew 154 is tightened into the cage 152 to lock the orientation of thecage 152 with respect to the pedicle screw 150.

The pedicle screw 150 has a head 160 and a shank 162. The head 160 has aconvex semispherical underside that engages the cage 152 in any of avariety of relative orientations to provide the polyaxial couplingdescribed previously. The head 160 also has a hexagonal recess 164designed to receive a hexagonal end of a pedicle screw driver (not shownin FIG. 7), which will be shown and described subsequently. The shank162 has a plurality of threads 166 that rotate into threaded engagementwith the tapped pedicle. The pedicle screw 150 also has a bore (notshown) extending through the shank 162 and the head 160 to receive anyof the guide wires 70, 72, 78 to facilitate guiding of the pedicle screw150 into engagement with the corresponding pedicle.

The cage 152 has a base 168 in which an aperture 170 is formed. Theaperture 170 is sized such that the shank 162 of the pedicle screw 150may be inserted through the aperture 170. The head 160 of the pediclescrew 150 then rests on a concave semispherical surface of the base 168,within which the head 160 is polyaxially rotatable. The cage 152 alsohas a pair of arms 172 that extend from the base 168, generally parallelto each other. Each of the arms 172 has a slot 174 and an exteriorrecess 176. The slots 174 pass through the arms 172 to communicate withthe slots 174. Each of the arms 172 has an inward-facing surface onwhich a plurality of threads 178 are formed to receive the set screw154. The arms 172 define recesses therebetween, and the recesses formends of a trough in which the rod portion 146 is able to rest.

As shown, the set screw 154 has a hexagonal recess 180 that enables theset screw 154 to be rotated by a driver that will be shown and describedsubsequently. The set screw 154 also has an outward-facing surface onwhich a plurality of threads 182 are formed to enable the set screw 154to rotate into threaded engagement with the cage 152. Once the rodportion 146 is positioned between the arms 172 of the cage 152, the setscrew 154 may be tightened to press the rod portion 146 against the head160 of the pedicle screw 150, thereby resisting further relativerotation between the cage 152 and the pedicle screw 150.

Upon assembly, the cannula 142, which is shown in exploded form in FIG.7, will have a proximal end 190 and a distal end 192. The cannula 142may be dimensioned such that the proximal end 190 protrudes above theskin, while the distal end 192 is securable to the cage 152 and isinsertable through the skin along with the cage 152. The cannula 142includes a first blade 194 and a second blade 196, which may besubstantially identical to each other. Each of the blades 194, 196 has aproximal end 198 corresponding to the proximal end 190 of the cannula142, and a distal end 200 corresponding to the distal end 192 of thecannula 142.

Each proximal end 198 has a proximal tab 202, and each distal end 200has a distal tab 204. Each proximal tab 202 has a locking ridge 206 thatprotrudes generally outward, and extends generally circumferentially.Each proximal tab 202 is also elongated, with a thin cross section thatpermits bending toward and away from the axis (not shown) of thecannula. Each distal tab 204 has bends 208 that cause the distal tab 204to jut outward, while remaining generally parallel with the remainder ofthe corresponding blade 194 or 196.

Each of the distal tabs 204 is insertable through the slot 174 of theadjacent arm 172 of the cage 152 when the corresponding blade 194 or 196is tilted to position the proximal end 198 inward relative to the distalend 200. Once the distal tabs 204 have passed through the slots 174,rotation of the blades 194 or 196 back to a position generally parallelto each other, and to the axis of the cage 152, causes the distal tabs204 to lie within the exterior recesses 176 of the arms 172 such thatthe bends 208 are unable to slide back through the slots 174. Thus, theblades 194, 196 are then in a locked configuration, and cannot bedetached from the cage 152 until they are again moved to the unlockedconfiguration, i.e., tilted to position the proximal ends 198 inward.

As long as the blades 194, 196 remain generally parallel to each other,the distal end 192 of the cannula 142 remains secured to the cage 152.Thus, the distal tabs 204 form a docking element that removably securesthe cannula 142 to the connecting element 140. The abutment member 144serves to keep the blades 194, 196 parallel to each other to keep thecannula 142 in assembled form and to simultaneously keep the cannula 142secured to the cage 152 by keeping the blades 194, 196 from rotatinginto the unlocked configuration. When the cannula 142 is secured to thecage 152, the cannula 142 is in its “docked configuration.” When thecannula 142 is removed from the cage 152, the cannula 142 is in its“undocked configuration.”

As shown, the abutment member 144 is generally disc-shaped with acentral opening 212 and an open side 214 that provides access to thecentral opening 212. The abutment member 144 also has an interior recess216 in communication with the central opening 212. Furthermore, theabutment member 144 has a pair of arcuate slots 218 that extend aroundopposing portions of the central opening 212 and are generally coaxialwith the central opening 212. The arcuate slots 218 are sized to receivethe first and second blades 194, 196 and to keep the first and secondblades 194, 196 generally parallel to each other, and perpendicular tothe abutment member 144. Thus, the blades 194, 196 are unable to pivotto the unlocked configuration and the cannula 142 maintains a generallytubular shape.

After the distal ends 200 of the blades 194, 196 are coupled to the cage152, the proximal ends 198 may be inserted through the arcuate slots 218of the abutment member 144. Each of the locking ridges 206 has awedge-like profile. Accordingly, as the locking ridges 206 pass throughthe arcuate slots 218, the proximal tabs 202 are urged to bend inward.Once the locking ridges 206 move out of the arcuate slots 218, theproximal tabs 202 snap back to an undeflected orientation, and thelocking ridges 206 are then positioned outboard of the arcuate slots 218to interfere with withdrawal of the proximal tabs 202 from the arcuateslots 218. Thus, the proximal tabs 202 act as a locking mechanism thatrestricts withdrawal of the abutment member 144 from around the cannula142.

After the blades 194, 196 have been inserted into the arcuate slots 218,the abutment member 144 may be positioned at any of a range of positionsalong the cannula 142. Thus, upon implantation of the pedicle screw 150in the corresponding pedicle, the abutment member 144 will abut theoutward-facing surface of the patient's skin through which the cannula142 passes. The abutment member 144 helps to stabilize the cannula 142with respect to the tissues it passes through.

Referring to FIG. 8, a perspective view illustrates the connectingelement 140, the cannula 142, the abutment member 144, and the rodportion 146 of FIG. 7, in assembled form. The shank 162 of the pediclescrew 150 has been inserted through the aperture 170 such that the head160 of the pedicle screw 150 rests against the base 168 of the cage 152.The rod portion 146 has been positioned between the arms 172 and the setscrew 154 has been rotated into engagement with the threads 166 of thearms 172 to keep the rod portion 146 in place and restrict furtherrotation of the cage 152 relative to the pedicle screw 150.

The distal tabs 204 have also been inserted through the slots 174 of thearms 172 of the cage 152, and the blades 194, 196 have been rotated intothe locked configuration. The proximal ends 198 of the blades 194, 196have been inserted through the arcuate slots 218 of the abutment member144 to keep the blades 194, 196 in assembled form to define the cannula142, and to keep the cannula 142 secured to the cage 152. When one orboth of the blades 194, 196 are oriented in the unlocked configuration,the blades 194, 196 may still be said to define the cannula 142,although the cannula 142 then has a tapered shape.

Once assembled, the cannula 142 has slots 220 extending along its entirelongitudinal length, along opposite sides of the cannula 142. The slots220 extend to the cage 152, and are therefore contiguous with therecesses defined by the arms 172 of the cage 152. Upon implantation ofthe pedicle screw 150, the slots 220 will extend along the entiresubcutaneous length of the cannula 142. Therefore, the rod portion 146may be inserted percutaneously through the slots 220 along a directiontransverse to the axis of the cannula 146, and may then be moved throughthe slots 220 along the anterior direction 16, directly into the troughof the cage 152.

Referring to FIG. 9, a perspective view illustrates a screw insertiontool 230 according to one embodiment of the invention. In the embodimentof FIG. 9, the screw insertion tool 230 has a driver 232 designed torotate the pedicle screw 150 into threaded engagement with thecorresponding tapped pedicle, and a countertorque member 234 thatmaintains the orientation of the cage 152 during rotation of the pediclescrew 150.

The driver 232 has a handle 236 designed to be rotated by hand, and ashank 238 extending from the handle 236. The shank 238 has a proximalend 240 and distal end 242 shaped to drive the pedicle screw 150. Thedistal end 242 has a hexagonal projection 244 that fits into thehexagonal recess 164 of the head 160 of the pedicle screw 150. Thedriver 232 also has a bore 246 sized to receive any of the guide wires70, 72, 78; the bore 246 extends through at least a portion of the shank238 and, optionally, through all or part of the handle 236 to permit thescrew insertion tool 230 to be easily guided along each of the guidewires 70, 72, 78.

The countertorque member 234 has a bore 248 that extends along itsentire length, through which the shank 238 of the driver 232 passes. Thebore 248 is large enough to permit easy relative rotation between thedriver 232 and the countertorque member 234. The countertorque member234 also has a generally tubular shape with a proximal end 250 and adistal end 252. The proximal end 250 has a plurality of longitudinalridges 254 designed to be gripped by a user's fingers to restrictrotation of the countertorque member 234. The distal end 252 has aplurality of threads 256 designed to threadably engage the threads 178of the arms 172 of the cage 152.

Thus, the distal end 252 of the countertorque member 234 can be rotatedinto engagement with the cage 152 to secure the countertorque member 234to the cage 152, thereby allowing a user to hold the longitudinal ridges254 to keep the cage 152 stationary during rotation of the driver 232.The countertorque member 234 also has longitudinal slots 258 thatprovide access to the bore 248 of the countertorque member 234 forcleaning or other purposes.

Referring to FIG. 10, a perspective view illustrates the screw insertiontool 230 of FIG. 9, in engagement with the assembly of FIG. 8, excludingthe rod portion 146 and the set screw 154. The threads 256 of the distalend 252 have been rotated into engagement with the threads 178 of thearms 172, and the hexagonal projection 244 has been inserted into thehexagonal recess 164 of the head 160 of the pedicle screw 150. The screwinsertion tool 230 is thus ready to implant the pedicle screw 150 intothe corresponding tapped pedicle.

In the alternative to the embodiment illustrated in FIGS. 9 and 10, ascrew insertion tool may have a countertorque member that functionsindependently of threaded engagement with the cage 152. For example, analternative countertorque member (not shown) may have et projectionsthat slide into the recesses between the arms 172, or engage otherfeatures of the cage 152, to prevent relative rotation between the cage152 and the countertorque member.

Referring to FIG. 11, a perspective view illustrates the screw insertiontool 230 in use to implant the assembly of FIG. 8, excluding rodportions 146 and set screws 154, over the first guide wire 70 of FIG. 2.The handle 236 may be used to actuate the connecting element 140, thecannula 142, and the abutment member 144 along the first guide wire 70.Upon contact of the pedicle screw 150 with the tapped pedicle 30 (notshown in FIG. 11), the handle 236 is rotated while the countertorquemember 234 is restrained from rotation via application of pressure onthe longitudinal ridges 254. Thus, the pedicle screw 150 is rotated intoengagement with the pedicle while keeping the cage 152, the cannula 142,and the abutment member 144 at a relatively constant orientation. Asshown, the cannula 142 is oriented such that the slots 220 generallyface in the cephalad direction 12 and the caudal direction 14.

As also shown, a second connecting element 260 has been implanted in thepedicle 50 of the second vertebra 26 (not shown in FIG. 11). A secondcannula 262 and a second abutment member 264 have been secured to thesecond connecting element 260 in a manner similar to that of the cannula142 and the abutment member 144. A third connecting element 270 has beenimplanted in the pedicle of the third vertebra (not shown in FIG. 11). Athird cannula 272 and a third abutment member 274 have been secured tothe third connecting element 270 in a manner similar to that of thecannula 142 and the abutment member 144. The second connecting element260, cannula 262, and abutment member 264 and the third connectingelement 270, cannula 272, and abutment member 274 may be substantiallyidentical to the connecting element 140, the cannula 142, and theabutment member 144, as shown in FIGS. 7 and 8.

Referring to FIG. 12, a perspective view illustrates a fascia clippingtool 280 according to one embodiment of the invention. As shown, thefascia clipping tool 280 has a first member 282 and a second member 284pivotably secured to the first member 284 through the use of a pin 286.The first member 282 has a finger loop 288 designed to receive a user'sfinger, and a blade 290 extending at a predefined angle from theremainder of the first member 282. Similarly, the second member 284 hasa finger loop 292 and a blade 294. The blades 290, 294 haveinwardly-oriented sharp edges that provide a scissoring effect when theblades 290, 294 are brought into a parallel configuration.

Referring to FIG. 13, a perspective view illustrates the fascia clippingtool 280 of FIG. 12 inserted into the cannula 142 of FIG. 11 to severthe adjoining fascia (not shown). The skin between the cannulas 142,262, 272 need not be severed; rather, only the subcutaneous fascia iscut to provide unimpeded percutaneous access to the cages 152 of theconnecting elements 150, 260, 270. The open side 214 and the interiorrecess 216 of each of the abutment members 144, 264, 274 provides theappropriate range of relative motion in the cephalad and caudaldirections 12, 14 for the first and second members 282, 284 to permitrelatively easy cutting of the fascia with little or no damage to thesurrounding tissue (not shown).

Referring to FIG. 14, a perspective view illustrates a rod insertiontool 300 according to one embodiment of the invention. As shown, the rodinsertion tool 300 has a handle 302 shaped to be grasped by hand, and ashank 304 extending from the handle 302. The handle 302 has a knob 306that can be rotated by hand to control retention of a rod (not shown inFIG. 14) by the rod insertion tool 300. The shank 304 has a proximal end308 secured to the handle 302 and a distal end 310 that receives and issecurable to the end of the rod.

More precisely, the distal end 310 may have a rod coupling 312 securableto the rod through the use of a mechanism such as a collet or gripper.Such a mechanism may be actuated by rotating the knob 306. According toalternative embodiments of the invention, an interference fit or anothersimilar mechanism may be used to retain the rod in such a manner thatthe rod can be removed when a threshold removal force is applied. Theshank 304 has a plurality of slots 314 distributed along the length ofthe shank 304 to provide access to a bore (not shown) of the shank 304for cleaning or other purposes.

Referring to FIG. 15, a perspective view illustrates the rod insertiontool 300 of FIG. 14 secured to a rod 316 to facilitate manual insertionof the rod 316 through the cannulas 142, 262, 272 of FIG. 11. As shown,the rod 316 has a leading end 317 and a trailing end 318 secured to therod coupling 312 of the rod insertion tool 300. Prior to insertionunderneath the skin, the rod 316 may be contoured based on themorphology of the patient's spine so that the rod 316 will maintain theproper lordotic angle between the first vertebra 24, the second vertebra26, and the third vertebra. Alternatively, the rod 316 may bepre-lordosed to provide a lordotic angle suitable for most patients. Therod 316 may optionally be selected from a kit (not shown) containingmultiple, differently angled rods.

The leading end 317 is first inserted through the skin (not shown) ofthe patient by inserting the leading end 317 through the proximal end190 of the cannula 142, and through the central opening 212 of theabutment member 144. Once underneath the skin, the handle 302 ismanipulated to insert the leading end 317 through the opening formed inthe fascia, through the slots 220 of the second cannula 262, and throughat least one slot 220 of the third cannula 272 and/or through at leastone recess of the cage 152 of the third connecting element 270. Then,the rod 316 may be detached from the rod insertion tool 300.

Referring to FIG. 16, a perspective view illustrates a rod seating tool320 according to one embodiment of the invention. As shown, the rodseating tool 320 has a handle 322 shaped to be gripped by hand, and ashank 324 extending from the handle 322. The shank 324 has a proximalend 326 adjacent to the handle 322 and a distal end 328 shaped to pushthe rod 316 into place. More precisely, the distal end 328 may have ablade 330 with a generally thin cross section. The blade 330 mayterminate in an arcuate recess 332 with a radius matching that of therod 316.

Referring to FIG. 17, a perspective view illustrates the rod seatingtool 320 of FIG. 16 inserted into the second cannula 262 of FIG. 11 tohelp seat the rod 316 in the cages 152 of the connecting elements 140,260, 270. As shown, the distal end 328 of the rod seating tool 320 maysimply be inserted through the second cannula 262 until the arcuaterecess 332 of the blade 330 abuts the rod 316. Then, pressure is appliedvia the handle 322 to urge the rod 316 to slide along the slots 220, inthe anterior direction 16 until the rod 316 is seated generally withinthe troughs of the cages 152 of the connecting elements 140, 260, 270.The distal end 328 may similarly be inserted into the cannula 142, thethird cannula 272, or any combination of the cannulas 142, 262, 272until the rod 316 has been positioned to pass through all of the cages152.

Referring to FIG. 18, a perspective view illustrates a rod holding tool18 according to one embodiment of the invention. The rod holding tool 18is designed to grip the rod 316 to permit translation of the rod 316along its axis or rotation of the rod 316 about its axis. As embodied inFIG. 18, the rod holding tool 18 has first handle 342, a second handle344, a central body 346, a shank 348, a pin 350, a first leaf spring352, a second leaf spring 354, and a pair of screws 356.

The first handle 342 has a proximal end 360 and a distal end 362. Theproximal end 360 has a transverse extension 364 that facilitatesgripping of the first handle 342, for example, with the fingers of onehand. The proximal end 360 also has a hole 366 with threads designed toreceive threads (not shown) of the corresponding screw 356. The distalend 362 has a blade 368 that is pivotably coupled to the central body346 by the pin 350.

The second handle 344 has a proximal end 370 and a distal end 372. Theproximal end 370 has a hole (not shown) similar to the hole 366 of theproximal end 360 of the first handle 342. The distal end 372 may beformed as a single piece with the central body 346. The central body 346has a slot 374 that receives the blade 368 of the distal end 362 of thefirst handle 342. The pin 350 passes through the slot 374 to extendthrough the blade 368, thereby providing the pivotable coupling betweenthe central body 346 and the first handle 342. The central body 346 alsohas a projection 376 that extends generally distally.

The shank 348 has a proximal end 380 at which the shank 348 is securedto the projection 376 of the central body 346, and a distal end 382designed to grip the rod 316 in response to pressure applied to squeezethe first and second handles 342, 344 together. More precisely, thedistal end 382 has an arcuate recess 384 with a radius matched to thatof the rod 316, and an arcuate extension 386 with a radius equal orsimilar to that of the arcuate recess 384.

The shank 348 also has a stationary arm 387 and a sliding arm 388, eachof which has a generally half-circular cross sectional shape. Thestationary arm 387 is rigidly attached to the projection 376, and thesliding arm 388 is slidably coupled to the stationary arm 387. Thearcuate extension 386 is on the stationary arm 387, and the arcuaterecess 384 is on the sliding arm 388. The sliding arm 388 is coupled tothe blade 368 of the first handle 342 within the central body 346 suchthat pivotal motion of the first handle 342 urges the sliding arm 388 toslide distally along the stationary arm 387.

The first leaf spring 352 has a fixed end 390 secured to the firsthandle 342 by the corresponding screw 356, and a coupled end 392 coupledto the second leaf spring 354. Similarly, the second leaf spring 354 hasa fixed end 394 secured to the second handle 344 by the other screw 356,and a coupled end 396 coupled to the coupled end 392 of the first leafspring 352. The coupled ends 392, 396 may be interlocked in aninterdigitated manner that permits relative rotation of the coupled ends392, 396. Thus, the leaf springs 352, 354 cooperate to provide resilientforce urging the first and second handles 342, 344 to move apart,thereby urging the distal end 382 of the shank 348 to release the rod316 in the absence of force urging the handles 342, 344 together.

In order to use the rod holding tool 340, a portion of the rod 316 mayfirst be positioned to abut the arcuate surface of the arcuate extension386. When the first and second handles 342, 344 are squeezed together,for example, by hand, the sliding arm 388 slides distally along thestationary arm 387. As the sliding arm 388 slides along the stationaryarm 387, the arcuate recess 384 moves toward the arcuate extension 386until the arcuate surface of the arcuate recess 384 is contiguous withthe arcuate surface of the arcuate extension 386. The arcuate recess 384then cooperates with the arcuate extension 386 to capture the rod 316 sothat the rod holding tool 340 can be used to axially rotate or translatethe rod 316, as desired.

Referring to FIG. 19, a perspective view illustrates the rod holdingtool 340 of FIG. 18 inserted into the second cannula 262 of FIG. 11 tofurther manipulate the rod 316. As shown, the distal end 382 of theshank 348 has been inserted through the second cannula 262 to positionthe arcuate extension 386 adjacent to the rod 316. The first and secondhandles 342, 344 have also been squeezed together to slide the arcuaterecess 384 against the rod 316 to capture the rod 316. Thus, the rod 316can be translated or rotated in any direction. More particularly, if therod 316 is not yet rotated to the proper orientation to pass properlythrough the cages 152, the rod 316 may be rotated axially through theuse of the rod holding tool 340. The rod 316 may also be translatedaxially if needed. Fluoroscopy or other known methods may be used tocheck the position and orientation of the rod 316 with respect to thecages 152.

Referring to FIG. 20, a perspective view illustrates a set screw driver400 according to one embodiment of the invention. As shown in FIG. 20,the set screw driver 400 has a handle 402 and a shank 404 extending fromthe handle 402. The handle 402 has a pair of oppositely disposedtransverse extensions 406 that protrude to facilitate manual grippingand rotation of the handle 402. The shank 404 has a proximal end 408adjacent to the handle 402 and a distal end 410 designed to transmittorque to the set screw 154. The distal end 410 may have a hexagonalprojection 412 insertable into the hexagonal recess 180 of the set screw154.

Referring to FIG. 21, a perspective view illustrates the set screwdriver 400 of FIG. 20 inserted into the cannula 142 of FIG. 11 totighten the corresponding set screw 154 to retain the rod 316 within thecorresponding cage 152. The set screws 154 may be applied after the rod316 has been properly positioned with respect to the cages 152.

The hexagonal projection 412 may first be inserted into the hexagonalrecess 180 of the set screw 154. Then, the handle 402 may be gripped andused to insert the set screw 154 into position adjacent to the threads178 of the arms 172 of the cage 152 of the connecting element 140. Thehandle 402 may then be rotated clockwise to cause the threads 182 of theset screw 154 to rotate into engagement with the threads 178. The handle402 may be rotated clockwise until the set screw 154 presses firmlyagainst the rod 316 to keep the rod 316 in place within thecorresponding cage 152, and to restrict further rotation of the cage 152with respect to the corresponding pedicle screw 150. All three of theset screws 154 may be positioned and tightened in this manner tocomplete assembly of the posterior spinal fusion system.

In addition to the set screw driver 400 of FIGS. 20 and 21, acountertorque member (not shown) may be provided. Such a countertorquemember may engage the cage 152 to keep the cage 152 from rotating whilethe set screw 154 is tightened.

Referring to FIG. 22, a perspective view illustrates the fully assembledposterior spinal fusion system including the connecting elements 140,260, 270 and the rod 316, with the cannulas 142, 262, 272 still securedto the cages 152 of the connecting elements 140, 260, 270, but with theabutment members 144, 264, 274 removed from the cannulas 142, 262, 272.The abutment members 144, 264, 274 may be removed from the cannulas 142,262, 272 by squeezing the proximal tabs 202 of each cannula 142, 262,272 together, for example, with the thumb and forefinger of a hand. Thelocking ridges 206 are thereby moved into alignment with the arcuateslots 218 of the abutment members 144, 264, 274 so that the abutmentmembers 144, 264, 274 can be withdrawn along the posterior direction 18from the corresponding cannulas 142, 262, 272, respectively.

As mentioned previously, once the abutment members 144, 264, 274 havebeen removed, the blades 194, 196 of each cannula 142, 262, 272 may bepivoted into the unlocked configuration. The distal tabs 204 may then bewithdrawn from the slots 174 of the arms 172 of the cages 152, and outof the patient's body. Then, the incisions made to accommodate thecannulas 142, 262, 272 may be closed and treated through the use ofmethods known in the art.

Referring to FIG. 23, a perspective view illustrates the completedposterior spinal fusion system. In addition to the first and secondvertebrae 24, 26, FIG. 23 illustrates a third vertebra 428 superior tothe second vertebra 26. The third vertebra 428 has features similar tothose set forth in the description of the first and second vertebrae 24,26. Most pertinently, the third vertebra 428 has pedicles 430 withsaddle points 432.

As shown, the pedicle screw 150 of the first connecting element 140 isimplanted in the pedicle 30 of the right side of the first vertebra 24,the pedicle screw 150 of the second connecting element 260 is implantedin the pedicle 50 of the right side of the second vertebra 26, and thepedicle screw 150 of the third connecting element 270 is implanted inthe pedicle 430 of the right side of the third vertebra 428. The rod 316passes through the troughs of the cages 152 in a manner that preservesthe proper lordosis of the spine 10. The set screws 154 have beenrotated into engagement with the cages 152 and tightened to keep the rod316 in place within the troughs of the cages 152 and to substantiallyeliminate rotation of the cages 152 relative to their respectivevertebrae 24, 26, 428.

The connecting elements 140, 260, 270 thus cooperate with the rod 316 torestrict relative motion of the vertebrae 24, 26, 428 to form aposterior vertebral fusion system. If desired, a similar system may beimplanted in the left-side pedicles 30, 50, 430 of the vertebrae 24, 26,428 through the method set forth previously to provide a bilateralsystem. Additionally, the present invention is not limited to athree-level fusion system, but may be used to fuse any number ofvertebrae together. To fuse more than three vertebrae together, thesteps set forth above may simply be repeated for each additionalvertebra, and the rod may be inserted through the skin via a firstcannula, and then percutaneously inserted through three or moreadditional cannulas.

A variety of alternative embodiments of the invention may be used inplace of the method and components illustrated in FIGS. 1-23. Forexample, a variety of different connecting elements known in the art maybe used in place of the connecting elements 140, 260, 270 shown anddescribed previously. Polyaxially rotatable cages are an optionalfeature of such connecting elements. Cannulas different from thecannulas 142, 262, 272 set forth above may be used, and need not beformed of multiple separate pieces, but may instead be single piecestructures. Such cannulas may have slots that terminate toward theirproximal ends.

A variety of different docking elements may be used in place of thedistal tabs 204 and the slots 174. Such docking elements may includethreaded engagement, collets, pin-and-locking-groove systems,interference fit couplings, snap-fit couplings, and the like.Additionally, a variety of locking mechanisms may be used in place ofthe proximal tabs 202. Such locking mechanisms may include lockingmembers securable to the proximal ends 190 of the cannulas 142, 262, 272to interfere with withdrawal of the abutment members 144, 264, 274therefrom, or locking members movably coupled to the proximal ends 190.Additionally, a wide variety of interfaces may be provided between eachcannula 142, 262, 272 and the corresponding abutment member 144, 164,274 to restrict withdrawal of the abutment members 144, 264, 274 fromthe cannulas 142, 262, 272.

Furthermore, each of the instruments set forth previously, including thescrew insertion tool 230, the fascia clipping tool 280, the rodinsertion tool 300, the rod seating tool 320, the rod holding tool 340,and the set screw driver 400, may be replaced with an alternativelyconfigured tool that performs a similar function. The steps recitedabove need not necessarily be performed in the order provided, but mayinstead be rearranged, and some steps may be omitted and/or other stepsmay be added, to provide alternative methods within the scope of theinvention.

According to one alternative embodiment of the invention, a connectingelement may have a cage pre-attached to a cannula that provides accessto the cage. Such an alternative embodiment will be shown and describedin greater detail in connection with FIG. 24.

Referring to FIG. 24, a perspective view illustrates a cannula 442 and acage 452 according to one alternative embodiment of the invention inwhich the cannula 442 and the cage 452 are initially secured together.The cage 452 may be part of a connecting element like the connectingelements 140, 260, 270 set forth previously. Accordingly, the cage 452may be polyaxially coupled to a pedicle screw like the pedicle screw 150of FIG. 7, and may be designed to receive a rod portion 146 like that ofFIG. 7. The cage 452 may also receive a set screw 154 like that of FIG.7 to keep the rod portion 146 in place and restrain pivotal relativemotion between the cage 452 and the pedicle screw 150.

As shown in FIG. 24, the cage 452 has a base 168 with an aperture 170designed to receive the pedicle screw 150. The cage 452 has a pair ofarms 472 extending from the base 168. The arms 472 need not have slots174 or exterior recesses 176 like the arms 172 of the cage 152 of FIG.7. However, each of the arms 472 does have threads 478 that face inwardto receive the set screw 154.

The cannula 442 has a generally tubular shape with a proximal end 490and a distal end 492. The cannula 442 includes a first blade 494 and asecond blade 496 positioned opposite the first blade 494. Each of theblades 494, 496 has a proximal end 498 that is substantially free, and adistal end 500 pre-attached to the corresponding arm 472 of the cage452. In the embodiment of FIG. 24, the distal ends 500 are formed as asingle piece with the arms 472, and are separated from the arms 472 byfrangible portions 504 of the distal ends 500. The cannula 442 has apair of slots 520 positioned opposite to each other to permitpercutaneous insertion of the rod 316 therein, as described inconnection with the previous embodiment.

Each frangible portion 504 may take the form of a necked-down regiondesigned to fracture in response to application of a certainpre-established threshold linear force or angular moment. Moreprecisely, each frangible portion 504 may fracture in response to forcetending to tilt the blades 494, 496 to push the proximal ends 498inward, toward the axis of the cannula 442. Thus, the frangible portions504 define a frangible coupling between the cannula 442 and the cage452.

In use, the cannula 442 and the cage 452 may be used in a manner similarto that set forth in FIGS. 1-23. However, the cannula 442 and the cage452 need not be secured together, since they are formed as a singlepiece. Additionally, no abutment member may be necessary, although anabutment member (not shown) somewhat similar to the abutment member 144may optionally be used to maintain the proper relative displacement ofthe blades 494, 496 during use. After implantation of the rod 316,removal of the blades 494, 496 from the cage 452 may be accomplished bytilting the blades 494, 496 inward as described previously to fracturethe frangible portions 504, thereby permitting separation of the blades494, 496 from the cage 452.

According to other alternative embodiments (not shown), blades may bepre-attached to a cage in a manner that does not require the blades tobe formed as a single piece with the cage. For example, the blades maybe welded, mechanically fastened, or otherwise pre-attached to the cage.Such embodiments may optionally have frangible portions. Alternatively,the blades may be removable in other ways, such as via removal of amechanical fastener.

The foregoing description discloses a number of different elements thatmay be combined in various ways to provide a number of alternativeimplantable systems. Although the foregoing examples relate toimplantation of a posterior spinal fusion system, the present inventionmay be applied to a wide variety of implants, within and outside theorthopedic area.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. It isappreciated that various features of the systems and methods describedabove can be mixed and matched to form a variety of other alternatives.As such the described embodiments are to be considered in all respectsonly as illustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

The invention claimed is:
 1. A system for providing access to a spine ofa patient, the system comprising: a first connecting element implantablein a first vertebra of a spine; and a first cannula adapted to receiveat least a portion of a spinal fusion rod therealong, the first cannulacomprising: a first blade; and a second blade discrete from the firstblade; wherein the first and second blades are configured to beassembled together substantially parallel to each other and mated withthe first connecting element, without being directly connected to oneanother, in order to provide the first cannula such that the firstcannula has a distal end terminating at the connecting element, wherebythe first cannula provides access to the spine when the first connectingelement is implanted in the first vertebra of the spine; and wherein thefirst and second blades are independently detachable from the firstconnecting element such that the first and second blades areindependently removable from the patient.
 2. The system of claim 1,wherein the connecting element comprises a pedicle screw implantable ina pedicle of the first vertebra, and a cage polyaxially movable withrespect to the pedicle screw.
 3. The system of claim 1, wherein thefirst and second blades are configured to be disassembled from oneanother without removing the distal end from within the patient.
 4. Thesystem of claim 3, wherein each of the first and second blades comprisesa locked configuration, in which the blade is secured to the connectingelement, and an unlocked configuration, in which the blade is removablefrom the connecting element, wherein each of the first and second bladesis movable between the locked and unlocked configurations in response torotation of the blade with respect to the connecting element.
 5. Thesystem of claim 4, wherein each of the first and second blades ismovable between the locked and unlocked configurations in response torotation of the blade about an axis substantially perpendicular to alongitudinal axis of the first cannula.
 6. The system of claim 1,further comprising an abutment member configured to engage the first andsecond blades to restrict relative motion between the first and secondblades.
 7. The system of claim 6, wherein the abutment member islockable with respect to the first and second blades by a lockingmechanism that restricts withdrawal of the abutment member from thefirst and second blades.
 8. The system of claim 7, wherein the lockingmechanism comprises a plurality of proximal tabs of the first and secondblades, wherein the proximal tabs are bendable to permit withdrawal ofthe abutment member from the first and second blades.
 9. The system ofclaim 1, further comprising an abutment member encircling at least aportion of the first cannula to abut an exterior skin surface of thepatient, wherein the abutment member is movable along the first cannulato define a variable subcutaneous length of the first cannula.
 10. Thesystem of claim 9, wherein the abutment member is shaped such that acombined length of the first cannula and the abutment member does notchange in response to motion of the abutment member along the firstcannula.
 11. The system of claim 1, wherein the first and second bladesare shaped such that, when positioned to define the first cannula, thefirst and second blades provide a first slot in a side wall of the firstcannula.
 12. The system of claim 11, wherein the first and second bladesare further shaped such that, when positioned to define the firstcannula, the first and second blades provide a second slot in the sidewall, wherein the second slot is arranged with respect to the first slotto permit passage of a rod through the first cannula along a directiontransverse to a longitudinal axis of the first cannula.
 13. The systemof claim 12, wherein the distal end is insertable into the patientproximate the spine such that each of the first and second slots extendsunbroken along an entire subcutaneous length of the cannula.
 14. Thesystem of claim 1, further comprising a second cannula securable to asecond connecting element implantable in a second vertebra of the spine,and a third cannula securable to a third connecting element implantablein a third vertebra of the spine, wherein the first, second, and thirdcannulas cooperate to facilitate attachment of a rod to the first,second, and third connecting elements to restrict relative motion of thefirst, second, and third vertebrae.
 15. The system of claim 1, whereinthe first and second blades have arcuate profiles, whereby the firstcannula is defined by a partially cylindrical shape.
 16. The system ofclaim 1, wherein the first and second blades each have a distal endincluding a tab insertable into a corresponding slot of the firstconnecting element.
 17. The system of claim 1, further comprising anabutment member configured to prevent the first and second blades frombecoming disconnected from the first connecting element.
 18. A systemfor providing access to a spine of a patient, the system comprising: acannula adapted to receive at least a portion of a spinal fusion rodtherealong, the cannula comprising a proximal end and a distal endinsertable into the patient proximate the spine, the distal endcomprising a docking element discrete from and securable to a connectingelement implantable in a first vertebra of the spine; wherein thedocking element is receivable by the connecting element in both a dockedconfiguration and an undocked configuration, the distal end beingsecured to the connecting element in the docked configuration, and thedistal end being received by and removable from the connecting elementin the undocked configuration, and wherein the docking element ismovable between the docked and undocked configurations in response torotation about an axis substantially perpendicular to a longitudinalaxis of the cannula.
 19. The system of claim 18, wherein the connectingelement comprises a pedicle screw implantable in a pedicle of the firstvertebra, and a cage polyaxially movable with respect to the pediclescrew, wherein the docking element is configured to dock with the cage.20. The system of claim 19, wherein the cannula comprises: a firstblade; and a second blade discrete from the first blade; wherein thefirst and second blades are positionable substantially parallel to eachother to provide the first cannula; wherein each of the first and secondblades comprises a locked configuration, in which the blade is securedto the connecting element, and an unlocked configuration, in which theblade is removable from the connecting element.
 21. The system of claim18, wherein the docking element includes a plurality of tabs, each ofthe first and second blades comprising at least one of the tabs at adistal end thereof, the tabs enabling rotation of the blades between thelocked configuration and the unlocked configuration.
 22. The system ofclaim 18, further comprising an abutment member configured to engage thefirst and second blades to restrict relative motion between the firstand second blades to restrict motion of the blades to the unlockedconfiguration.
 23. The system of claim 22, wherein the abutment memberis lockable with respect to the first and second blades by a lockingmechanism that restricts withdrawal of the abutment member from thefirst and second blades.
 24. The system of claim 23, wherein the lockingmechanism comprises a proximal tab of each of the first and secondblades, wherein the proximal tabs are bendable to permit withdrawal ofthe abutment member from the first and second blades.
 25. A system forproviding access to a spine of a patient, the system comprising: acannula adapted to receive at least a portion of a spinal fusion rodtherealong, the cannula comprising a distal end insertable into thepatient proximate the spine and securable to a connecting elementimplantable in a first vertebra of the spine, the cannula furthercomprising a proximal end and a longitudinal axis extending between theproximal and distal ends; and an abutment member encircling at least aportion of the cannula and adapted to abut an outward facing surface ofskin of the patient, the entire length of the abutment member along thelongitudinal axis of the cannula being disposed between the proximal anddistal ends of the cannula, wherein the abutment member is adapted tomove along the cannula from the proximal end to the distal end such thatthe abutment member can be moved to a position abutting the outwardfacing surface of skin when the distal end of the cannula is secured tothe connecting element, whereby a variable subcutaneous length of thecannula is defined, and wherein a combined length of the cannula and theabutment member does not change in response to motion of the abutmentmember along the cannula.
 26. The system of claim 25, wherein thecannula comprises: a first blade; and a second blade discrete from thefirst blade; wherein the first and second blades are positionablesubstantially parallel to each other to provide the cannula.
 27. Thesystem of claim 26, wherein the abutment member is configured to engagethe first and second blades to restrict relative motion between thefirst and second blades.
 28. The system of claim 25, wherein theabutment member is lockable with respect to the cannula by a lockingmechanism that restricts withdrawal of the abutment member from thecannula.
 29. The system of claim 28, wherein the locking mechanismcomprises a plurality of proximal tabs of the cannula, wherein theproximal tabs are bendable to permit withdrawal of the abutment memberfrom the cannula.
 30. The system of claim 25, wherein the cannulacomprises a first slot extending longitudinally along a side wall of thecannula.
 31. The system of claim 25, wherein the cannula comprises adocking element that couples the cannula to a connecting elementimplantable in a vertebra of the spine, wherein the docking elementcomprises a frangible coupling configured to fracture in response toapplication of a threshold force against the frangible coupling topermit removal of the distal end from the connecting element.
 32. Asystem for providing access to a spine of a patient, the systemcomprising: a cannula comprising: a first component; and a secondcomponent discrete from the first component; and an abutment member;wherein the first and second components are configured to be assembledto a connecting element implantable in a first vertebra of the spine,wherein each of the first and second components has a distal endreceivable in the connecting element in a receiving position and alocked position, each of the first and second components being movablebetween the receiving position and the locked position in response torotation about an axis substantially perpendicular to a longitudinalaxis of the cannula, wherein the abutment member configured to engagethe first and second components to restrict relative motion between thefirst and second components, and wherein the abutment member is lockablewith respect to the first and second components by a locking mechanismthat restricts withdrawal of the abutment member from the first andsecond blades.
 33. The system of claim 32, wherein the first componentcomprises a first blade, and the second component comprises a secondblade, wherein the first and second blades are positionablesubstantially parallel to each other to provide the cannula.
 34. Thesystem of claim 33, wherein the distal end comprises a docking elementsecurable to a connecting element implantable in a first vertebra of thespine, wherein each of the first and second blades is secured to theconnecting element in the locked position and received within butremovable from the connecting element in the receiving position.
 35. Thesystem of claim 32, wherein the locking mechanism comprises a pluralityof proximal tabs of the first and second components, wherein theproximal tabs are bendable to permit withdrawal of the abutment memberfrom the first and second components.
 36. The system of claim 32,wherein the first and second components have arcuate surfaces, wherebythe cannula is defined by a partially cylindrical shape.
 37. A systemfor providing access to a spine of a patient, the system comprising: acannula adapted to receive at least a portion of a spinal fusion rodtherealong, the cannula having a longitudinal axis and comprising adistal end insertable into the patient proximate the spine, and aproximal end, the distal end comprising a docking element securable to aconnecting element implantable in a first vertebra of the spine; and anabutment member encircling at least a portion of the cannula, theabutment member having an abutment surface substantially normal to thelongitudinal axis, the abutment surface adapted to abut an exterior skinsurface of the patient, wherein the abutment member is adapted to movealong the cannula from the proximal end to the distal end such that theabutment member can be moved to a position wherein the abutment surfaceabuts the exterior skin surface when the docking element is secured tothe connecting element implanted in the first vertebra of the spine,whereby a variable subcutaneous length of the cannula is defined. 38.The system of claim 37, wherein the connecting element comprises apedicle screw implantable in a pedicle of the first vertebra, and a cagepolyaxially movable with respect to the pedicle screw.
 39. The system ofclaim 37, wherein the abutment member is lockable with respect to thecannula by a locking mechanism that restricts withdrawal of the abutmentmember from the cannula.
 40. The system of claim 39, wherein the lockingmechanism comprises a plurality of proximal tabs of the cannula, whereinthe proximal tabs are bendable to permit withdrawal of the abutmentmember from the cannula.
 41. The system of claim 37, wherein theabutment member is shaped such that a combined length of the cannula andthe abutment member does not change in response to motion of theabutment member along the cannula.
 42. The system of claim 37, whereinthe cannula further comprises a first slot portion formed in a side wallof the cannula.
 43. The system of claim 42, wherein the cannula furthercomprises a second slot portion formed in the side wall, wherein thesecond slot is arranged with respect to the first slot to permit passageof a rod through the cannula along a direction transverse to thelongitudinal axis of the cannula.
 44. The system of claim 43, whereinthe distal end is insertable into the patient proximate the spine suchthat each of the first and second slots extends unbroken along theentire subcutaneous length.
 45. The system of claim 37, wherein thedocking element comprises a frangible coupling configured to fracture inresponse to application of a threshold force against the frangiblecoupling to permit removal of the distal end from the connectingelement.
 46. The system of claim 37, wherein the cannula comprises: afirst blade; and a second blade discrete from the first blade; whereinthe first and second blades are positionable substantially parallel toeach other to provide the cannula, and wherein the abutment member isconfigured to engage the first and second blades to restrict relativemotion between the first and second blades.
 47. A system for providingaccess to a spine of a patient, the system comprising: a cannula adaptedto receive at least a portion of a spinal fusion rod therealong, thecannula comprising a distal end insertable into the patient proximatethe spine and securable to a connecting element implantable in a firstvertebra of the spine, the cannula further comprising a proximal end anda first slot extending longitudinally between the distal and proximalends; and an abutment member encircling at least a portion of thecannula, the abutment member having an abutment surface extendingsubstantially laterally from an outer surface of the cannula, theabutment surface adapted to abut an exterior skin surface of thepatient, wherein the abutment member is adapted to move along thecannula from the proximal end to the distal end such that the abutmentmember can be moved to a position wherein the abutment surface abuts theexterior skin surface when the distal end of the cannula is secured tothe connecting element implanted in the first vertebra of the spine,whereby a variable subcutaneous length of the cannula is defined. 48.The system of claim 47, wherein the abutment member is lockable withrespect to the cannula by a locking mechanism that restricts withdrawalof the abutment member from the cannula.
 49. The system of claim 48,wherein the locking mechanism comprises a plurality of proximal tabs ofthe cannula, wherein the proximal tabs are bendable to permit withdrawalof the abutment member from the cannula.
 50. The system of claim 47,wherein the abutment member is shaped such that a combined length of thecannula and the abutment member does not change in response to motion ofthe abutment member along the cannula.
 51. The system of claim 47,wherein the cannula further comprises a second slot portion formed inthe side wall, wherein the second slot is arranged with respect to thefirst slot to permit passage of a rod through the cannula along adirection transverse to a longitudinal axis of the cannula.
 52. Thesystem of claim 51, wherein the distal end is insertable into thepatient proximate the spine such that each of the first and second slotsextends unbroken along the entire subcutaneous length.
 53. The system ofclaim 47, wherein the cannula comprises a docking element that couplesthe cannula to a connecting element implantable in a vertebra of thespine, wherein the docking element comprises a frangible couplingconfigured to fracture in response to application of a threshold forceagainst the frangible coupling to permit removal of the distal end fromthe connecting element.
 54. The system of claim 47, wherein the cannulacomprises: a first blade; and a second blade discrete from the firstblade; wherein the first and second blades are positionablesubstantially parallel to each other to provide the cannula, and whereinthe abutment member is configured to engage the first and second bladesto restrict relative motion between the first and second blades.
 55. Amethod for spinal implant placement, comprising: securing a firstconnecting element to a first vertebra of a spine of a patient's body,the first connecting element having a first passageway device formed asa single piece with the first connecting element and extendingproximally therefrom, such that the first passageway device extendsproximally from the secured first connecting element through a firstincision in the skin of the patient, the first passageway devicedefining a first longitudinal passageway therein extending along acentral longitudinal axis of the first passageway device; inserting aleading end of a rod into the body of the patient through the firstincision in the skin; moving the leading end of the rod underneath anunbroken portion of the skin on a first side of the first passagewaydevice; securing the rod to the first connecting element; fracturing afrangible portion between the first passageway device and the firstconnecting element; and removing the first passageway device from thebody of the patient while the first connecting element remains implantedin the first vertebra.
 56. The method of claim 55, wherein the firstconnecting element comprises a pedicle screw having a cage connectedthereto for receiving the rod, the step of securing the first connectingelement to the first vertebra comprising implanting the pedicle screw ina pedicle of the first vertebra.
 57. The method of claim 55, wherein thefrangible portion comprises a necked-down region designed to fracture inresponse to application of a certain pre-established linear force orangular moment.
 58. The method of claim 55, further comprising:inserting a cutting tool along the first longitudinal passageway; andusing the cutting tool to cut subcutaneous tissue underneath theunbroken portion of the skin on the first side of the first passagewaydevice.
 59. The method of claim 55, further comprising engaging thefirst passageway device with an abutment member.
 60. The method of claim59, further comprising moving the abutment member along the firstpassageway device.
 61. The method of claim 60, further comprising movingthe abutment member to a position abutting an outward facing surface ofthe skin of the patient.
 62. The method of claim 59, further comprisingrestricting withdrawal of the abutment member from the first passagewaydevice.
 63. The method of claim 55, wherein the first passageway deviceis defined by a first blade and a second blade positioned adjacent toone another and providing the first longitudinal passagewaytherebetween.
 64. The method of claim 63, wherein the frangible portionbetween the first passageway device and the first connecting elementcomprises a first frangible portion connecting the first blade to thefirst connecting element and a second frangible portion connecting thesecond blade to the first connecting element, and wherein the step offracturing the frangible portion between the first passageway device andthe first connecting element comprises fracturing the first and secondfrangible portions.
 65. The method of claim 64, wherein fracturing thefirst and second frangible portions comprises tilting each of the firstand second blades with respect to the first connecting element.
 66. Themethod of claim 65, wherein tilting each of the first and second bladeswith respect to the first connecting element comprises tilting the firstand second blades inwardly towards the central longitudinal axis of thefirst passageway device.
 67. The method of claim 63, further comprisingmaintaining the first and second blades in a substantially parallelrelationship with an abutment member.
 68. The method of claim 67,wherein the abutment member has a central opening, and wherein the stepof inserting the leading end of the rod into the body of the patientcomprises inserting the leading end of the rod through the centralopening of the abutment member.
 69. The method of claim 68, wherein theabutment member has a C-shaped wall partially surrounding the centralopening and defining an open side, the open side being positioned on asecond side of the first passageway device, the second side beingopposed to the first side across the central longitudinal axis of thefirst passageway device.
 70. The method of claim 55, further comprisingmaintaining opposing sides of the first incision apart around the firstlongitudinal passageway with the first passageway device.
 71. The methodof claim 55, further comprising securing a second connecting element toa second vertebra of the spine, the second connecting element having asecond passageway device coupled thereto and extending proximallytherefrom, such that the second passageway device extends proximallyfrom the secured second connecting element through a second incision inthe skin of the patient, the second passageway device defining a secondlongitudinal passageway therein extending along a central longitudinalaxis of the second passageway device, wherein the unbroken portion ofthe skin on the first side of the first passageway device extendsbetween the first incision and the second incision.
 72. The method ofclaim 71, further comprising maintaining opposing sides of the firstincision apart around the first longitudinal passageway with the firstpassageway device, and maintaining opposing sides of the second incisionapart around the second longitudinal passageway with the secondpassageway device.
 73. The method of claim 71, wherein the firstpassageway device defines a transverse opening therethrough, and whereinthe step of moving the leading end of the rod underneath the unbrokenportion of the skin comprises passing the leading end of the rod throughthe transverse opening while the rod extends in a transverse orientationto the central longitudinal axis of the first passageway device.
 74. Themethod of claim 73, wherein the transverse orientation of the rodincludes a trailing end of the rod being positioned above the skin on asecond side of the first passageway device while the leading end of therod is positioned underneath the unbroken portion of the skin on thefirst side of the first passageway device, the second side being opposedto the first side across the central longitudinal axis of the firstpassageway device.
 75. The method of claim 71, wherein the step ofmoving the leading end of the rod underneath the unbroken portion of theskin comprises moving the leading end of the rod subcutaneously towardsthe second passageway device or towards the second connecting element.76. The method of claim 71, further comprising securing a thirdconnecting element to a third vertebra of the spine, the thirdconnecting element having a third passageway device coupled thereto andextending proximally therefrom, such that the third passageway deviceextends proximally from the secured third connecting element through athird incision in the skin of the patient, the third passageway devicedefining a third longitudinal passageway therein extending along acentral longitudinal axis of the third passageway device.
 77. A methodfor spinal implant placement, comprising: securing a first connectingelement to a first vertebra of a spine of a patient's body, the firstconnecting element having a first blade and a second blade formed as asingle piece with the first connecting element and extending proximallytherefrom, such that each of the first and second blades extendsproximally from the secured first connecting element through a firstincision in the skin of the patient, the first and second blades beingpositioned adjacent to one another to define a first longitudinalpassageway therealong between the first and second blades; securing asecond connecting element to a second vertebra of the spine, the secondconnecting element having a third blade and a fourth blade formed as asingle piece with the second connecting element and extending proximallytherefrom, such that each of the third and fourth blades extendsproximally from the secured second connecting element through a secondincision in the skin of the patient, the third and fourth blades beingpositioned adjacent to one another to define a second longitudinalpassageway therealong between the third and fourth blades; inserting aleading end of a rod into the body of the patient through the firstincision and between the first and second blades; moving the leading endof the rod underneath an unbroken portion of the skin extending betweenthe first and second incisions; securing the rod to the first and secondconnecting elements; uncoupling the first and second blades from thefirst connecting element by fracturing a first frangible portion betweenthe first blade and the first connecting element and by fracturing asecond frangible portion between the second blade and the firstconnecting element; and removing the first and second blades from thebody of the patient while the first connecting element remains implantedin the first vertebra.
 78. The method of claim 77, wherein the firstconnecting element comprises a first pedicle screw and the secondconnecting element comprises a second pedicle screw, each of the firstand second pedicle screws having a respective cage connected thereto forreceiving the rod, wherein the step of securing the first connectingelement to the first vertebra comprises implanting the first pediclescrew in a pedicle of the first vertebra, and wherein the step ofsecuring the second connecting element to the second vertebra comprisesimplanting the second pedicle screw in a pedicle of the second vertebra.79. The method of claim 77, wherein the step of moving the leading endof the rod underneath the unbroken portion of the skin comprisespositioning the rod in a transverse orientation to a centrallongitudinal axis extending between the first and second blades, suchthat, while the leading end of the rod is positioned underneath theunbroken portion of the skin, a trailing end of the rod is positionedabove the skin on an opposing side of the central longitudinal axis fromthe unbroken portion of the skin.